All digital image convertors in the field of radiology (e.g. image amplifiers, flat-panel detectors with indirect or direct conversion, etc.) convert imaging X-ray quanta into digital grayscale values via various intermediate steps. In the process, the corresponding convertor layers of the image convertor filter an inherently stochastic radiation field from an X-ray tube and convert a radiation field, which has been attenuated in a modulated fashion by an examination object (e.g. a patient), into a diagnosable X-ray image within the scope of DQE (detective quantum efficiency). During the scope of these different conversion types, systematic and stochastic artifacts are always introduced as well into the useful signal and should be minimized as far as possible. In this context, the so-called “ghosting” is a known phenomenon. Part of the image signal of the preceding X-ray image remains in the memory of the detector and thus contributes to the useful signal of the subsequent X-ray image in an additive fashion. This in turn is expressed occasionally by distracting artifacts, which can moreover result in a misdiagnosis.
According to the prior art, there are a number of different approaches for tackling the problem of ghosting: By selecting suitable layer thicknesses and layer designs of e.g. a scintillator (convertor layer), it is possible to make a compromise between resolution on the one hand and the tendency for ghosting on the other hand. Additionally, a so-called reset light can be utilized for partial deletion of the detector memory, as disclosed in e.g. “Photodiode gain calibration of flat dynamic x-ray detectors using reset light” by Burkhard A. Groh, Bernhard Sandkamp, Mathias Hoernig, Volker K. Heer, Falko Busse and Thierry Ducourant, Proc. SPIE, vol. 4682, pages 438 to 446, Medical Imaging 2002: Physics of Medical Imaging, Larry E. Antonuk; Martin Yaffe; Eds. Within the scope of digital image processing, it is possible to undertake image data correction by means of a suitable model function using e.g. the knowledge of the physical causes of the ghosting, which image data correction re-subtracts contrast-rich ghosts in particular from the X-ray image; this is known from, for example, “Lag correction model and ghosting analysis for an indirect-conversion flat-panel imager” by Noor Mail, Peter O'Brien and Geordi Panga, Journal of Applied Clinical Medical Physics, Vol. 8, No. 3, 2007, pages 137 to 146.
Due to their physical causes, the ghosting effects relax relatively quickly, and so a further method for preventing these artifacts is to plan for sufficient time between two recordings. To this end, a system computer in modern X-ray image systems prescribes a fixed mandatory pause, during which no further images can be taken. Furthermore, methods are also known, for example, in which a so-called de-ghost scan with a very high dose and a clear beam path leads to artificial overloading of the detector, and this produces a homogeneous, ghost-free empty image.